The present invention relates to a polyazo compound or a salt thereof, and a dye-based polarization film containing the same.
Polarization films are produced by adding iodine and dichromatic dye as a polarization element into a polarization film substrate such as a drawn and oriented polyvinyl alcohol-based film, an oriented polyene-based film produced by de-hydrochloric acid of a polyvinyl chloride film or dehydration of a polyvinyl alcohol film, and the like. Among them, iodine-based polarization films manifest a problem of decrease in abilities thereof under high temperature and high humidity conditions, since they have poor endurance to heat and poor endurance to water though they are excellent in the initial polarization ability. Some methods are studied for enhancing such endurances, such as a method in which treatment is effected with an aqueous solution containing formaldehyde or boric acid, a method In which a polymer film having low water vapor permeability is used as a protective film, and the like,. However, these methods are not sufficient yet.
On the other hand, dye-based polarization films using a dichromatic dye as a polarization element generally poor In initial polarization ability though they art excellent in endurance to heat and water as compared with iodine-based polarization films. Therefore, there is a desire for polyazo dyes used in a polarization film excellent in the initial polarization ability.
The present inventors have investigated dyes which have excellent dyeing property in producing a polarization film, are excellent in polarization ability. durability under high temperature and high humidity conditions and light resistance, and cover a region of from 500 to 580 nm in a polarization film used for a liquid crystal projector and the like, the polarization film being obtained by orientation and adsorption of a dichromatic dye in a polymer film, Resultantly, they have found that a specific polyazo compound or salt thereof attains the above-mentioned object. Thus, the present invention was completed.
Namely, the present Invention provides a polyazo compound or salt thereof of the following formula (I): 
wherein,
A represents a naphthyl having 1 to 3 sulfos or a phenyl having 1 to 2 hydrophilic groups selected from sulfo and carboxyl and optionally having a lower alkyl or lower alkoxy,
B represents xe2x80x94NHCOxe2x80x94 or xe2x80x94Nxe2x95x90Nxe2x80x94,
n represents 0 or 1, provided that, when B represents xe2x80x94Nxe2x95x90Nxe2x80x94, n represents or
R1 to R6 are the same or different and represent hydrogen, lower alkyl or lower alkoxy, provided that, when n represents 0, R1 to R4 represent hydrogen or lower alkyl,
R7 represents hydrogen or sulfo,
D represents xe2x80x94Nxe2x95x90Nxe2x80x94 when B is xe2x80x94Nxe2x95x90Nxe2x80x94 and represents xe2x80x94NHCOxe2x80x94, xe2x80x94Nxe2x95x90Nxe2x80x94 or xe2x80x94NHxe2x80x94 when B is xe2x80x94NHCOxe2x80x94,
and E represents a phenyl optionally having 1 to 3 groups selected from hydroxyl amino, nitro, sulfo, carboxyl, lower alkyl and lower alkoxy.
The present invention further provides a dye-based polarization film obtainable by adding the above-mentioned polyazo compound or salt thereof into a polarization film substrate.
A in the above-mentioned formula (I) represents a naphthyl having 1 to 3 sulfos or a phenyl having 1 to 2 hydrophilic groups selected from sulfo and carboxyl and optionally having a lower alkyl or lower alkoxy. The lower alkyl or lower alkoxy is preferably a linear or branched group having 1 to 4 carbon atoms. Specific examples of the lower alkyl include methyl, ethyl, propyl and the like. Specific examples of the lower alkoxy include methoxy, ethoxy, propoxy and the like.
Examples of the phenyl represented by A include 2-, 3- or 4-sulfophenyl, 2-, 3- or 4-carboxyphenyl, 2,4- or 2,5-disulfophenyl, 3,5-dicarboxyphenyl, 2-carboxy-4- or -5-sulfophenyl, 2 - or 3-methyl-4-sulfophenyl, and the like. Among them, 4-sulfophenyl is preferable.
Examples of the naphthyl represented by A include 5-, 6-, 7- or 8-sulfo-2-naphthyl, 4-, 5-, 6- or 7-sulfo-1-naphthyl, 1,5-, 6,8-, 4,8-, 5,7- or 3,6-disulfo-2-naphthyl, 3,6- or 4,6-disulfo-1-naphthyl, and 1,5,7-, 3,6,8- or 4,6,8-trisulfo-2-naphthyl and the like. Among them, naphthyls having 2 to 3 sulfos are preferable, and disulfo-2-naphthyls such as 1,5-, 6,8-, 4,8-, 5,7- or 3,6-disulfo-2-naphthyl and the like are particularly preferable.
R1 to R6, which are the same as or different from each other, represent hydrogen, lower alkyl or lower alkoxy, provided that, when n represents , R1 to R4 represent hydrogen or lower alkyl, and do not represent a lower alkoxy. As the lower alkyl and lower alkoxy, linear or branched groups having 1 to 4 carbon atoms are preferable. As specific examples of the lower alkyl, methyl, ethyl. propyl and the like are listed. As specific examples of the lower alkoxy, methoxy, ethoxy, propoxy and the like are listed.
R1 to R6 preferably represent hydrogen or methyl.
R7 represents hydrogen or sulfo, and preferably hydrogen.
E represents a phenyl optionally having 1 to 3 groups selected from hydroxyl, amino, nitro, sulfo, carboxyl, lower alkyl and lower alkoxy. Examples of the lower alkyl and lower alkoxy include those exemplified as the substituent of the phenyl represented by A. E preferably represents 4-hydroxyphenyl or 4-aminophenyl.
A polyazo compound of the formula (I) wherein n represents 0 and B represents xe2x80x94NHCOxe2x80x94 or a salt thereof can be produced, for example, by methods described below.
First, an amide compound of the following formula (II): 
wherein, A, R1 and R2 are as defined above, is diazotized by reacting with sodium nitrite in an acidic aqueous medium under a condition of 5 to 40xc2x0 C. The resulted diazotized compound is reacted with an aniline compound of the following formula (III): 
wherein, R3 and R4 are as defined above, in an aqueous medium under conditions of 5 to 40xc2x0 C. and pH from 6 to 11, to obtain a monoazo compound. The resulted monoazo compound is diazotized by reacting with sodium nitrite in an acidic aqueous medium under a condition of 5 to 40xc2x0 C. The resulted second diazotized compound is reacted with a hydroxynaphthalene compound of the following formula (IV): 
wherein, R7 D and E are as defined above, in an aqueous medium under conditions of 5 to 40xc2x0 C. and pH from 6 to 11, to obtain an azo compound of the formula (I).
Examples of an azo compound of the formula (I) wherein n represents 0 and B represents xe2x80x94NHCOxe2x80x94 include 
and the like.
A polyazo compound of the formula (I) wherein n represents 0 and B represents xe2x80x94Nxe2x95x90Nxe2x80x94 or a salt thereof can be produced, for exampler by a method described below.
First, a disazo compound of the following formula (V): 
wherein, A, R1, R2, R3 and R4 are as defined above, is diazotized by reacting with sodium nitrite in an acidic aqueous medium under a condition of 5 to 40xc2x0 C. The resulted diazotized compound is reacted with a naphthol compound of the formula (TV) wherein D represents xe2x80x94Nxe2x95x90Nxe2x80x94 in an aqueous medium under conditions of 5 to 40xc2x0 C. and pH from 6 to 11, to obtain a polyazo compound of the formula (I) or salt thereof.
Examples of a polyazo compound of the formula (I) wherein n represents 0 and B represents xe2x80x94Nxe2x95x90Nxe2x80x94 include 
and the like.
A polyazo compound of the formula (I) wherein n represents 1 and B represents xe2x80x94NHCOxe2x80x94 or a salt thereof can be produced, for example, by a method described below.
First, a disazo compound of the following formula (VI): 
wherein, A and R1 to R6 are as defined above, is diazotized with sodium nitrite in an acidic aqueous medium under a condition of 5 to 40xc2x0 C. Then, the resulted diazotized compound is reacted with a naphthol compound of the above-described formula (IV) in an aqueous medium under conditions of 5 to 40xc2x0 C. and pH from 6 to 11, to obtain a polyazo compound of the formula (I) or a salt thereof.
As the compound of the formula (IV), compounds of the following formula (VII) or (VIII) 
wherein, R7 has the above-mentioned meaning, and R8 represents hydrogen, amino or hydroxyl, are preferable.
Specific examples of a compound of the formula (IV) include 
and the like.
Examples of a polyazo compound of the formula (I) wherein n represents 1, namely B represents xe2x80x94NHCOxe2x80x94 include 
and the like.
As examples of the salt of a polyazo compound (I) , alkali metal salts such as a lithium salt, sodium salt and potassium salt, an ammonium salt, and organic amine salts such as an ethanolamine salt and alkylamine salt, and the like are listed, When a polyazo compound of the formula (I) is added into a polarization film substrate, a compound in the form of a sodium salt is preferably used.
When a polyazo compound of the formula (I) or salt thereof is added into a polarization film substrate to give a polarization film, hue can be modified and polarization ability can be improved by combination with another organic dye. As the organic dye used in this case, any dye can be used as long as it has high dichroism. A polarization film suitably used in a liquid crystal projector can be produced, using a dye excellent in light resistance.
Specific examples of such organic dyes include the following compounds expressed by Color Index Generic Name.
C. I. Direct Yellow 12
C. I. Direct Yellow 28
C. I. Direct Yellow 44
C. I. Direct Orange 26
C. I. Direct Orange 39
C. I. Direct Orange 107
C. I. Direct Red 2
C. I. Direct Red 31
C. I. Direct Red 79
C. I. Direct Red 81
C. I. Direct Red 247
The dye-based polarization film of the present invention can be produced by adding a dichromatic dye comprising a polyazo compound of the formula (I) or a salt thereof or a dichromatic dye further comprising other organic dye, into a polymer film, polarization film substrate, by a known method. Examples of this polymer film include polymer films made of polyvinyl alcohol-based resins, polyvinyl acetate resins, ethylene/vinyl acetate (EVA) resins, nylon resin, polyester resins or the like Examples of the polyvinyl alcohol-based resin herein referred to include a partial or complete saponified polyvinyl acetate, that is polyvinyl alcohol; saponified substances of copolymers of vinyl acetate with other copolymerizable monomers, for example, olefins such as ethylene and propylene, unsaturated carboxylic acids such as crotonic acid, acrylic acid, methacrylic acid and maleic acid, unsaturated sulfonic acids, vinyl ethers, and the like, such as saponified EVA resins; polyvinyl formal and polyvinyl acetal obtained by denaturing polyvinyl alcohol with an aldehyde, and the like. As the polarization film substrate, polyvinyl alcohol-based films, particularly, a polyvinyl alcohol film is suitably used from the standpoints of adsorbing property and orientation property of a dye.
For adding a dichromatic dye into such a polymer film, a method of dyeing a polymer film is usually adopted. Dyeing can be effected, for example, according to the following method. First, a dichromatic dye is dissolved in water to prepare a dye bath. The concentration of a dye in the dye bath is not particularly restricted, but usually selected in the range from 0.0001 to 10% by weight. If necessary, a dyeing aid may be used. For example, it is suitable to use sodium sulfate in an amount of 0.1 to 10% by weight in a dye bath. A polymer film is immersed into the dye bath thus prepared, and dyeing is effected. The dyeing temperature is preferably from 40 to 80xc2x0 C. Orientation of a dichromatic dye is conducted by stretching a polymer film. As the stretching method, any method such as a wet method, dry method and the like may be adopted, for example. Stretching of a polymer film may be conducted before dyeing or after dyeing.
A polymer film obtained by adding and orientating a dichromatic dye is subjected, if necessary to a post treatment such as boric acid treatment and the like according to a known method. Such a post treatment is effected for improving light transmittance, degree of polarization and endurance of a polarization film. Though conditions of the boric acid treatment differ depending on the kind of a polymer film used and the kind of a dye used, the boric acid treatment is generally effected using a boric acid aqueous solution having a concentration of from 1 to 15% by weight, preferably from 5 to 10% by weight at a temperature ranging from 30 to 80xc2x0 C., preferably from 50 to 80xc2x0 C. Further, if necessary, a fix treatment may be together conducted using an aqueous solution containing a cationic polymer compound.
A protective film excellent in optical transparency and mechanical strength can be pasted on one surface or both surfaces of thus obtained dye-based polarization film, to give a polarization plate. The material forming a protective film may be which conventionally used. For example, films composed of a fluorine resin such as an ethylene tetrafluoride/propylene hexafluoride copolymer, polyester-based films, polyolefin-based films, polyamide-based films and the like may be used, in addition to cellulose acetate-based films and acrylic films.